WASHINGTON (AFP) – US astronomers said Wednesday they have discovered an Earth-sized planet that they think might be habitable, orbiting a nearby star, and believe there could be many more planets like it in space.

The planet, found by astronomers at the University of California, Santa Cruz, and the Carnegie Institution of Washington, is orbiting in the middle of the "habitable zone" of the red dwarf star Gliese 581, which means it could have water on its surface.

Liquid water and an atmosphere are necessary for a planet to possibly sustain life, even it it might not be a great place to live, the scientists said.

The scientists determined that the planet, which they have called Gliese 581g, has a mass three to four times that of Earth and an orbital period of just under 37 days.

Its mass indicates that it is probably a rocky planet and has enough gravity to hold on to an atmosphere, according to Steven Vogt, professor of astronomy and astrophysics at the University of California, Santa Cruz, and one of the leaders of the team that discovered the planet.

If Gliese 581g has a rocky composition similar to Earth's, its diameter would be about 1.2 to 1.4 times that of the Earth, the researchers said.

The surface gravity would be about the same or slightly higher than Earth's, so that a person could easily walk upright on the planet, Vogt said.

Gliese 581g was discovered by scientists working on the Lick-Carnegie Exoplanet Survey, during 11 years of observing the red dwarf star Gliese 581, which is only 20 light years from Earth.

For astronomers, eleven years of observation is considered a short time and 20 light years, which is roughly 117.5 trillion miles, rather close. The sun is around eight and a half light minutes from Earth.

"The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common," said Vogt.

The planet is tidally locked to its star, meaning that one side is always facing the star and basking in perpetual daylight, and the other is in perpetual darkness because it faces away from the star.

With surface temperatures decreasing the further one goes toward the dark side of the planet and increasing as one goes into the light side, the most habitable part of the new planet would be the line between darkness and light, which is known as the "terminator".

The researchers estimate that the average surface temperature of the planet would be between -24 and 10 degrees Fahrenheit (-31 to -12 degrees Celsius).

But actual temperatures would range from "blazing hot on the side facing the star to freezing cold on the dark side," they said.

The findings, which will be published in the Astrophysical Journal and posted online at arXiv.org, "offer a very compelling case for a potentially habitable planet," said Vogt.

"Any emerging life forms on the new planet would have a wide range of stable climates to choose from and to evolve around, depending on their longitude," Vogt said.

In their report, the scientists in fact announce the discovery of two new planets around Gliese 581, bringing the total number of known planets around this star to six.

That is the most yet discovered in a planetary system other than Earth's solar system.

Like planet's in Earth's solar system, the planets around Gliese 581 have nearly circular orbits.

Two previously detected planets around Gliese lie at the edges of the habitable zone, one on the hot side and one on the cold side of the star, and are probably not habitable.

The newly discovered planet g, however, lies right in the middle of the habitable zone.

"We had planets on both sides of the habitable zone -- one too hot and one too cold -- and now we have one in the middle that's just right," Vogt said, recalling the porridge that Goldilocks found in the children's story "The Three Bears."

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September 30, 20107:13 pm

greeney2

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The good news, its not to far away, the bad news is you would be 4762 years old by the time you get there. They do have a billboard only a few planets outside of town that says, "message board troublemakers, keep out".

September 30, 201010:14 pm

sandra

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With surface temperatures decreasing the further one goes toward the dark side of the planet and increasing as one goes into the light side, the most habitable part of the new planet would be the line between darkness and light, which is known as the "terminator".

Ah no thanks.

The surface gravity would be about the same or slightly higher than Earth's, so that a person could easily walk upright on the planet, Vogt said.

Well I am glad that is a requirment for it to be habitable.

“Living backwards!” Alice repeated in great
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“—but there’s one great advantage in it, that one’s
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September 30, 201010:50 pm

Aquatank

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20 light years out isn't bad its only about 40-80 years travel time at 50% light. So a Cold Fusion, Metastable Metallic Hydrogen, or Anti-matter powered photon rocket could get us there especially if we used Jupiter as a sling shot.

The question becomes one of a generation ship versus some kind of suspended animation sleeper ship. Personally I feel safer with the generation ship, by using a enclosed environment in the first place later generations would not feel as claustophobic living under a terraforming dome as earlier ones and would adapt easier planet side. And the planet orbiting Gliese 581 isn't very nice with only one side face the star.

October 2, 20107:42 am

SmokinJoe

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If they had a way to get us there and back (like 1yr/2yr tour of duties) I'd love to go.

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October 2, 20109:04 am

Ninor

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"greeney2" wrote: The good news, its not to far away, the bad news is you would be 4762 years old by the time you get there. They do have a billboard only a few planets outside of town that says, "message board troublemakers, keep out".

Well, that leaves you out, doesn't it greeney2? 😛

October 2, 20109:16 am

The_Joker

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This is all well and good but can the Government (All Governments) afford the gas to get there and back multiple times to build habitable housing colonies .. I think not .. this I'm sorry to say it is a pipe dream.

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Gunpowder, treason and plot.
I see no reason why gunpowder, treason
Should ever be forgot...

October 2, 20103:41 pm

Aquatank

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First of all to get there needs a place to build a ship, If we are talking aboout a colony ship it going to need to be big (try 2 to 4 times the size of a Nimitz class aircraft carrier) and built in space. That means building a space elevator to the construction facility, and noting that the colonists will need to carry a space elevator onboard to reach the planets surface. The ship also needs 3000+ colonists for proper continuation of the species without mutation as well hydroponic chemicals a vast seed vault, lots of fresh water and an onboard recycling facility. I'd suggest using "Cold Fusion"/Nuclear Effect reactors to power the ship. I think its worth it because we cannot keep all our eggs in one basket, sooner or later the sun will expand or we might get hit with a star x-ray burst, get hit with a nasty asteroid, have a super volcano blow up, have a human made device cause an extinction level disaster, get hit with a virus we can't stop etc etc etc. Its worth the cost of building.

October 3, 201012:52 am

_Billy_

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My question is, will they ever find intelligent life on the planet Earth?

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